The term 'GREEN DIGIT' is a combination of two crossword solutions: THUMB (5 letters) and DIGIT (5 letters). The term 'THUMB' refers to the THUMB on the human hand, which is the most opposable DIGIT and is used for grasping and holding objects. The term 'DIGIT' is a general term for any of the numbers 0-9. Together, the two terms form the phrase 'GREEN DIGIT', which is often used to refer to the GREEN digits on a digital display, such as those found on a calculator or computer monitor.